The equal channel angular extrusion/pressure (ECAE/ECAP) technique had been developed for twenties years, which provides novelty and effective means for producing ultrafine-grained materials with extraordinary mechanical properties. The mechanism is that the billets pass through two equal cross-section channels with intersecting at an angle by extruding, where the pure shear deformation takes place severely, and an intense plastic strain is introduced into the billets without changing the cross-section area; the considerable total strain can be obtained in a bulk material by the accumulating effects after repeatedly extruding, and the grain sizes are significant refined which results in micron-size or even submicron-size grains in the materials.
The ECAE technique has so far been mainly applied for experimentation and research work, and is mainly used as improving properties, increasing deformability, investigating the superplastic behaviors or the evolutions of microstructures and anisotropy.
Utilizing the unique characteristic of ECAE, appropriate different alloys are selected and carried out clad extrusion forming by means of ECAE, and the method enables alloys grains refining and enables ductility improving. Since the clad extrusion of the billets are performed accompanying by heating, the bonding of the clad interfaces is considerable reliable via diffusing process. At the same time, the dimensions of billets can be controlled accurately by means of ECAE, so the composites with exact dimensions are produced. Making use of the technical characteristic of ECAE, the layer-metal composites using different alloy systems are promising to develop, such as Mg, Al, Zn, Ti, Cu, Fe and their alloys as well as steel, etc, and different kinds of composite materials can be prepared utilizing the combining of these materials.
The advantages of the ECAE technical have attracted widely attentions in the industries, some industry applications are being explored and developed at present, and definite progresses has been made, such as the continuous confined strip shearing (C2S2) process based on ECAE is reported by Lee et al., where the strip is carried out continuous shearing by ECAE following rolling, so the metallic sheets are produced in a continuous mode and in a repeatable manner; in addition, the ECAE equipment with moving walls provides a direction for producing large dimension productions; while a new ECAE method with rotary-die remarkably simplified the difficulty of loading and unloading die process time after time, which permits a new extruding cycle to follow without billet removal and reinsertion. Obviously, ECAE technique is gradually developing to industrial applications.
As the rapidly development of aerospace, automobile industries, chemistry industries, architecture and electron industries, more and more rigorous properties demanding for the materials are required, and the conventional simplex materials encounter more and more difficulties in meeting the demands of the mechanical, chemical and electromagnetism properties aspects. While the composite materials not only combine the advantages of individual component materials but also possess some special functions which the simplex material is not possessing. So the composite materials pioneer one new approach of designing and producing materials, and have been widely applied in many industry technology fields. While the key of composite preparation stems from the development of cladding technique. The usual methods for fabricating composites mainly consist of cast, extrusion, roll cladding, explosive welding and explosive welding+rolling cladding, etc, and the application of the explosive welding is the most extensive one.
Though these cladding techniques have been applied in the practical manufacture and each possesses its own advantages, inevitably, there also exist some disadvantages. For example, the bonding interfaces of explosive welding composites easily take place curving so as to influence the bonding strength, and the dimensions of the productions are difficult to control accurately, in addition, this method entails a high cost and has a number of limitations; clad roll materials easily bend during the producing and the preparation is complicated; while the cast compound device is complex and the clad course is found to be difficult in controlling. So the new clad technique attracts more and more attentions. Recently, there are some new types of layer-metal clad technique, such as reverse solidification, pour clad, rolling following casting clad, spray-deposited clad technique, etc, which reflects new characteristics of high efficiency, low cost, consecution and short procedure in the layer-metal clad technique, also representing the new develop direction of the clad technique. But there are still faultinesses in the new techniques, which limit their applications in the practical industry, and many technology problems need resolving.
The main disadvantages of ordinary clad extrusion are: the thicknesses of walls both inside and outside along the length direction are often unsymmetrical due to the asymmetry metal flow during the extrusion. When the discrepancy of deformation resistance between inside and outside materials is large, there easily occurs wave in shape or bamboo knot in the joint interface even breaking in hard layer, so the selection and assembling of materials are greatly limited. While utilizing ECAE technique to prepare composite material of different alloys is one kind of new approach and new method, which is also a new cladding forming technique, and there has not corresponding reports being seen up to the present.